Mold cleaning sheet and method of producing semiconductor devices using the same

ABSTRACT

A cleaning sheet ( 29 ) is formed with a trough-hole ( 29   a ) at a portion corresponding to a cavity of a mold along with a slit ( 29   b ) or a flow cavity cut ( 29   c ) at every corner at an outer periphery of the through-hole ( 29   a ) and is placed between a first mold half and a second mold half of the mold to clean the inside of the mold, thereby improving the cleaning effect of the mold.

CROSS-REFERENCES

This is a continuation application of U.S. Ser. No. 12/494,891, filedJun. 30, 2009, which is a continuation application of U.S. Ser. No.11/431,508, filed May 11, 2006 (now U.S. Pat. No. 7,572,398), which is acontinuation application of U.S. Ser. No. 10/296,724, filed Nov. 26,2002 (now U.S. Pat. No. 7,384,582). This continuation application isrelated to U.S. Ser. No. 11/200,066, filed Aug. 10, 2005 (nowabandoned). The entire disclosures of all of the above-identifiedapplications are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a semiconductor-producing technique, and moreparticularly, to a technique effective for application to an improvementin cleaning effect on the inside of a mold for a semiconductor deviceand also on productivity.

BACKGROUND ART

In the resin molding step for resin molded-type semiconductor devices,resin molding is repeated several times, so that resin burrs and dirt,such as oil or dust, are accumulated in the inside of the mold, in whicha molding resin is filled, or in the cavities, runners and air vents ofa pair of top and bottom halves constituting the mold and also in a cullblock and its neighbor.

Such dirt adversely influences the quality of moldings and leads to alowering of releasability when a product is removed from the mold.Accordingly, it is necessary for a worker to clean the mold at intervalsof given shots.

However, the cleaning of a mold by a worker is a manual work, whichrequires much time. Thus, there is a demand for a technique wherein amold can be cleaned within a short time.

For a technique meeting the requirement, a method has been carried out,as stated in Japanese Laid-open Patent Application No. Hei 1(1989)-95010, wherein a lead frame not mounting a semiconductor chip(hereinafter referred to as dummy lead frame) is clamped between themain surfaces (faces) of a mold, and a cleaning resin formed of amelamine resin or the like is charged into the mold and hardened tocause dirt to be deposited on the cleaning resin surface, therebyremoving the dirt along with the cleaning resin.

Alternatively, there is known a method of directly pouring a cleaningresin into the cavity at a high pressure or normal pressure without useof any dummy lead frame or the like.

However, according to the first-mentioned technique, an expensive dummylead frame has to be used for cleaning, and not only this is poor ineconomy, but also a dummy lead frame of a specific shape matched with amold has to be set in position and clamped, so that precise positioningbetween the mold and the dummy lead frame becomes necessary. Moreover,with a molded resin for cleaning, the resin formed at cull and runnerportions is separated out of the lead frame and the removal of thisseparated resin from the mold requires much time, thus being poor inworking property. In addition, the separated cull and runner may becaught in a sliding portion of a molding apparatus, with the possibilityof causing mechanical breakdown.

In order to solve such problems as stated hereinabove, a technique setout below has been proposed.

As described in Japanese Laid-open Patent Application No. Hei 6(1994)-254866, the technique comprises the steps of clamping asheet-shaped cleaning member made of cotton cloth (non-woven fabric), inwhich a cleaning resin can be impregnated and permeated, between openedmold halves, and filling a cleaning resin in a molten state in thecavity of the closed mold.

As described in the known instance, when a cleaning resin in a fluidform is charged in such a state that the sheet, in which a cleaningresin and chemicals are able to be impregnated therein and permeatedtherethrough, is placed between the main surfaces (faces) of the top andbottom mold halves, an advantage is offered in that not only thepositioning accuracy required between the mold and the sheet can belowered, but also the cleaning resin and chemicals can be infiltrated ata portion where the sheet is sandwiched between the main surfaces of thetop and bottom mold halves, thereby permitting the mold to be cleaned.

In the technique, however, when the cleaning resin is filled in thecavity, the sheet-shaped member is vertically moved (lifted) within thecavity. This causes a phenomenon wherein the sheet-shaped member becomesresistant to the flow of the cleaning resin, not allowing the cleaningresin to be run to all corners of the cavity.

Eventually, dirt is left at the corners of the cavity, with theattendant problem that cleaning within the cavity becomesunsatisfactory.

It should be noted that the faces of the mold have recesses, such as aflow cavity (capable of escaping air or a molding resin to prevent airfrom being entrained from a gate and ensure well-balanced filling of themolding resin in the cavity) and an air vent, in communication therewithformed at corners of the outer periphery of the cavity.

However, where the molding is subjected to cleaning with use of acleaning sheet for a mold, the cleaning resin is unlikely to creep inthe corners of the cavity and vicinities thereof. As a result, thecleaning resin does not enter into the flow cavity and air vent, andthus the flow cavity and air vent cannot be cleaned. This arises theproblem of shortage of a molding resin being filled into the cavity uponmolding of a product after cleaning.

Further, if the molding resin is unlikely to creep in the corners of thecavity and vicinities thereof, the cleaning resin is not stuck atportions of the molding cleaning sheet corresponding to the cavitycorners and vicinities thereof. This presents the problem that aftercompletion of the cleaning, when the cleaning resin is removed from thefaces of the mold along with the mold cleaning sheet, the cleaning resinis partly left, which takes much time in removing the mold cleaningsheet and the cleaning resin from the faces.

In the faces of a mold for molding of SOP (small outline package) havingan elongated portion to be molded and QFN (quad flat non-leaded package)using a matrix frame, where the distance between the outer edge of acavity and the margin of the face is relatively small (e.g. where thedistance is 10 mm or below), the cleaning resin leaked from the cavityruns out of the mold cleaning sheet upon cleaning of the mold andattaches to over the side surfaces contiguous to the faces of the mold.

In this case, it takes much time to remove the cleaning resin from theside surfaces of the mold, with the attendant problem that theefficiency of the cleaning work lowers.

An object of the invention is to provide a mold cleaning sheet which isable to improve the cleaning effect of a mold and also improveproductivity through the reduction in time of a cleaning work and also amethod of producing semiconductor devices using the mold cleaning sheet.

The above and other objects and novel features of the invention willbecome apparent from the description of the present specification andthe attached drawings.

DISCLOSURE OF THE INVENTION

The invention provides a mold cleaning sheet which is placed between apair of first mold half and a second mold half of a mold so as to cleanthe inside of the mold wherein when placed between the first mold halfand the second mold half, the sheet entirely covers the faces of themold therewith and has a through-hole formed correspondingly to a cavityof the mold.

The invention also provides a cleaning method, which comprises the stepsof providing a mold cleaning sheet which entirely covers the faces of amold made of a first mold half and a second mold half and has athrough-hole formed correspondingly to a cavity of the mold, placing themold cleaning sheet on the entire faces of the mold so that thethrough-hole is in conformity with the cavity and clamping the moldcleaning sheet between the first mold half and the second mold half,supplying a cleaning resin to the cavity, making the cleaning resin passthrough the through-hole of the mold cleaning sheet to fill the cleaningresin in the cavity, and after solidifying the cleaning resin, releasingthe cleaning resin and the mold cleaning sheet from the mold.

Furthermore, the invention provides a molding method of a semiconductordevice, which comprises the steps of (a) providing first and second moldhalves having a face and a recess formed in the face, respectively, (b)providing a sheet having a through-hole and capable of being impregnatedand permeated with a cleaning resin, (c) clamping the sheet between thefaces of the first and second mold halves so that the position of thethrough-hole of the sheet is conform with the recesses of the first andsecond mold halves, (d) after the step (c), pouring a cleaning resin inthe recesses of the first and second mold halves, (e) after the step(d), removing the sheet and the cleaning resin from the first and secondmold halves, (f) providing a semiconductor chip having a plurality ofelectrodes on a main surface thereof, a conductor member, and aplurality of wires electrically connecting the plurality of electrodesof the semiconductor chip and the conductor member therewith, (g) afterthe step (e), accommodating in position the semiconductor chip and theplurality of wires in the recesses of the first and second mold halvesand sandwiching the conductor member between the faces of the first andsecond mold halves, and (h) after the step (g), pouring a molding resinin the recesses of the first and second mold halves so that thesemiconductor chip, the plurality of wires and part of the conductormember are molded.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing an example of a structure of atransfer molding apparatus for carrying out molding by use of a moldingcleaning sheet according to Embodiment 1 of the invention;

FIG. 2 is a view, partially in section, of a structure of a resinmolding unit of the transfer molding apparatus shown in FIG. 1;

FIG. 3( a) and FIG. 3( b) are views showing an instance of a moldcleaning sheet according to Embodiment 1 of the invention wherein FIG.3( a) is a plan view, and FIG. 3( b) is a sectional view taken along theline A-A;

FIG. 4 is a plan view showing an instance of a state where a moldcleaning sheet is placed on the face of a second mold half of a moldprovided at the resin molding unit shown in FIG. 2;

FIG. 5 is a view, partially in section, of an instance of a state incase where the mold is cleaned by use of the mold cleaning sheet shownin FIGS. 3( a) and 3(b);

FIG. 6 is a perspective view, partially in section, of an instance of astructure of a semiconductor device produced according to a method ofproducing a semiconductor device according to the invention;

FIG. 7 is a plan view showing an instance of a structure of a moldcleaning sheet according to Embodiment 2 of the invention;

FIG. 8 is a partially enlarged, plan view showing an instance of a statewhere the mold cleaning sheet shown in FIG. 7 is placed in a face of amold;

FIG. 9 is a plan view showing a structure of a mold cleaning sheet thatis a variation of the mold cleaning sheet shown in FIG. 7;

FIG. 10( a) and FIG. 10( b) are views showing an instance of a structureof a mold cleaning sheet according to Embodiment 3 of the inventionwherein FIG. 10( a) is a plan view and FIG. 10( b) is a sectional viewtaken along the line B-B of FIG. 10( a);

FIG. 11 is a plan view showing an instance of a state where the moldcleaning sheet shown in FIGS. 10( a) and 10(b) is placed on a face of amold; and

FIG. 12 is a partially enlarged, sectional view taken along the line C-Cof FIG. 11.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following embodiments, the same or similar parts or portions arenot repeatedly illustrated in principle except as otherwise hereinrequired.

Moreover, in the following embodiments, a plurality of sections orembodiments are separately described, if necessary, for convenience'ssake. Unless otherwise specified, such sections or embodiments are notmutually irrelative, but one is in relation with variations, details andsupplemental description of part or all of others.

In the following embodiments, where reference is made to the number andthe like parameters of elements (including the number, value, amount,range and the like), it should not be construed to limit, for example,the number to a specified one, but a larger or smaller number may beusable except where specified and where it is necessary to limit to aspecified number clearly in principle.

The embodiments of the invention are described in detail with referenceto the accompanying drawings. It will be noted that throughout thedrawings for illustrating the embodiments, like reference numeralsindicate like members having same function and are not repeatedlyexplained.

Initially, Embodiment 1 of the invention is illustrated. A transfermolding apparatus shown in FIG. 1 is of a multi-pot type, which is used,for example, for molding a semiconductor chip 24 shown in FIG. 6 andinner leads 20 and the like electrically connected to the semiconductorchip 24.

This transfer molding apparatus includes a first mold half 3 serving asa top mold half and a second mold half 4 paired therewith and serving asa bottom mold half, a resin molding unit 5 having the first mold half 3and the second mold half 4, a loader 1 transferring a work (which isherein a leaf frame obtained after completion of die bonding and wirebonding) to the resin molding unit 5, and an unloader 2 withdrawing thework from the resin molding unit 5. In the transfer molding apparatus,the lead frame bonded with the semiconductor chip 24 (see FIG. 6) istransferred from the loader 1, shown in FIG. 1, to the resin moldingunit 5, in which the semiconductor chip 24 is resin molded. It will benoted that QFP (quad flat package) 19, which is a resin-moldedsemiconductor device after completion of resin molding, is transferredwith the unloader 2 and accommodated therein.

Further, the resin molding unit 5 shown in FIG. 2 is provided with acavity 6 having a shape corresponding to a molded portion 22 of the QFR19 shown in FIG. 6, a cull 7, a runner 8, a pot 9, a plunger 10, ejectorplates 11, 15, ejector pins 12, 16, a gate 13, and an air vent 14.

As shown in FIG. 4, a plurality of cavities with a given shape, in whichthe semiconductor chips 24 are disposed, respectively, are formed at aface of the second mold half 4 of a mold 28 (see FIG. 2) (it should benoted that the cavities 6 are formed at a face 26 of the first mold half3, like the second mold half 4).

A plurality of cylindrical pots 9, wherein a molding resin in the formof tablets are set, are formed in position of the second mold half 4therethrough, and the first mold half 3 has the culls 7, as shown inFIG. 2, at portions corresponding to the pots 9.

Moreover, a plurality of runners communicating with the plurality ofcavities 6 are formed from the cull. In such a state that the first moldhalf 3 and the second mold half 4 are in intimate contact with eachother, the pot 9 is closed with the cull 7 at the upper side thereof,and the pots 9 respectively, communicate with the plurality of cavitiesthrough the culls 7 and the runners 8. It will be noted that the airvent 14 for permitting air in the cavity to escape to outside andcompletely fill the resin therein is formed at the outside of the cavity6.

Next, a mold cleaning sheet 17 (herein after referred to simply ascleaning sheet) of Embodiment 1 shown in FIGS. 3( a) and 3(b) is nowdescribed.

The cleaning sheet 17 is used for cleaning the inside of the mold 28 byplacing the cleaning sheet 17 between the first mold half 3 and thesecond mold half 4 of the mold 28 when the semiconductor chip 24 doesnot undergo molding. When placed between the first mold half 3 and thesecond mold half 4, the cleaning sheet 17 entirely covers the faces(parting faces other than the cavity) of the mold 28 therewith and isformed with through-holes 17 a corresponding to the cavities 6 of themold 28.

It should be noted that the through-holes 17 a formed in the cleaningsheet 17 of Embodiment 1 is formed substantially in the same shape as anopening 6 a of the cavity 6 (see FIG. 2).

More particularly, the through-hole 17 a is formed as havingsubstantially the same shape and size as or a square pattern that isslightly smaller in size than the opening 6 a of the first mold half 3and the second mold half 4.

In this condition, when cleaned, only the cleaning sheet 17 is clampedbetween the first mold half 3 and the second mold half 4, under which acleaning resin 25 shown in FIG. 5 is supplied to the cavity 6. Thecleaning resin 25 passes through the through-hole 17 a of the cleaningsheet 17 within the cavity 6, so that the cleaning resin 25 is filledthroughout the cavity 6 without lifting the cleaning sheet 17 throughthe resistance of the cleaning resin 25 within the cavity 6.

Accordingly, the inside or inner surfaces of the cavity 6 can besatisfactorily cleaned.

The cleaning sheet 17 of Embodiment 1 has such a size and shape as toentirely cover the face 26 of the second mold half 4 (which is true ofthe first mold half 3) as shown in FIG. 4.

More particularly, the cleaning sheet 17 is so formed as to have a sizesufficient to be guided with positioning wedges 18 which are provided atthe respective sides of the outer periphery of the face 20 of the secondmold half 4 and are used for positioning of the top and bottom moldhalves. In this state, for mounting of the cleaning sheet 17 on the face26 of the second mold half 4, the cleaning sheet 17 should be mounted inconformity with the positioning wedges 18 at the respective sides, andit is unnecessary to make high precision positioning with the mold 28.

The cleaning sheet 17 of Embodiment 1 is formed, for example, of 100%paper, cloth or a nonwoven fabric having a heat resistance andflexibility, of which it is preferred to form the sheet with a nonwovenfabric.

The thickness of the cleaning sheet 17 is, for example, at about 0.6 mmwhen the sheet is clamped between the first mold half 3 and the secondmold half 4.

The QFP 19 shown in FIG. 6 is an instance of a semiconductor device setup after molding with the transfer molding apparatus shown in FIG. 1.This device includes bonding wires 21 for electrical connection betweenelectrodes of a semiconductor chip 24 and corresponding inner leads 20,and the molded portion 22 formed by resin molding of the semiconductorchip 24, the inner leads 20 and the bonding wires 21, and a plurality ofouter leads 23 extended from individual inner leads 20 and serving asexternal terminals projecting from the molded portion 22 to outside. Therespective outer leads 23 are formed in a gull wing shape.

Next, a method of producing a semiconductor device of Embodiment 1 isnow described.

It is to be noted here that the method of producing the semiconductordevice comprises the steps of molding (resin molding) the semiconductorchip 24 by use of the transfer molding apparatus shown in FIG. 1, andcleaning the inside of the mold 28 of the transfer molding apparatususing the cleaning sheet 17 shown in FIGS. 3( a) and 3(b).

Initially, in the wire bonding step, the semiconductor chip 24 and theinner leads 20 of the lead frame, which is a work, are electricallyconnected by means of the bonding wires 21.

Thereafter, in the molding step, the semiconductor chip 24 and the innerleads 20 electrically connected with the semiconductor chip 24 areresin-molded with a molding resin along with the bonding wires 21.

The resin molding step in the molding step of Embodiment 1 isillustrated.

First, a solid molding resin (tablets) heated by means of a preheater isset on the plunger 10 shown in FIG. 2, and the lead frame wherein thesemiconductor chip 24 and the inner leads 20 are wire-bonded istransferred from the loader 1 shown in FIG. 1 to the resin molding unit5.

In this state, the second mold half 4 is moved closely toward the firstmold half 3, thereby forming a space, including the cavity 6, betweenthe first mold half 3 and the second mold half 4 of the mold 28.Thereafter, a molten molding resin is forced into the cull 7 by means ofthe plunger 10, with the result that the molding resin flows into thecavity 6 through the runner 8 and the gate 13.

Further, the molding resin filled in the cavity is heated and cured andis thus thermally hardened, followed by downward movement of the secondmold half for mold opening.

Subsequently, while the ejector plate 15 is downwardly moved, theejector plate 11 is upwardly moved. This permits the ejector pins 12, 16to be projected to complete the mold opening, and the resin-molded QFP(semiconductor device) 19 is removed. This resin molding is repeatedseveral hundreds of shots per day, so that the inside of the mold 28filling the molding resin, i.e. the faces of the first mold half 3 andthe second mold half 4 of the mold 28 (including the air vent 14, thecavity 6, the runner 8, the cull 7 and surrounding areas thereof) isaccumulated with resin burrs or dirt (deposits) such as oil or dust.

In order to remove the dirt, the mold 28 in the molding step should besubjected to the cleaning step.

It will be noted that the QFP 19 is subjected to a cutting step to cutthe lead frame, thereby completing the setup of the QFP 19 shown in FIG.6.

Next, the cleaning step (the cleaning procedure of a mold) of Embodiment1 is set forth.

A cleaning sheet 17 shown in FIGS. 3( a) and 3(b) is provided, which isformed of a nonwoven fabric and which entirely covers the face 26 of themold 28 and is formed with a through-hole 17 a corresponding to thecavity 6 of the mold 28.

Subsequently, the temperature of the mold 28 is set, for example, at170° C. to 180° C.

Thereafter, as shown in FIG. 4, the cleaning sheet 17 is disposedentirely over the face 26 so that the through-hole 17 a is set inconformity with the cavity 6, under which the second mold half 4 ismoved closely toward the first mold half 3.

The close movement permits the cleaning sheet 17 to be clamped betweenthe first mold half 3 and the second mold half 4, and the cleaning resin25 is subsequently supplied into the cavity 6.

As shown in FIG. 5, the cleaning resin 25 is made to pass through thethrough-hole 17 a of the cleaning sheet 17 and filled in the cavity 6 toevery corner thereof.

Subsequently, the cleaning resin 25 is hardened, followed by downwardmovement of the second mold half 4 to release the first mold half 3 andthe second mold half 4 for the release of the mold.

Furthermore, the ejector plate 15 is downwardly moved and the ejectorplate 11 is upwardly moved. This permits the ejector pins 12, 16 to beprojected thereby completing the mold release.

The cleaning resin 25 and the cleaning sheet 17 are released from themold 28.

More particularly, the cleaning sheet 17 and the cleaning resin 25resin-molded on the sheet are removed.

In this way, the mold 28 is cleaned in the inside thereof.

It will be noted that for molding again after cleaning of the mold 28 inthe inside thereof by use of the cleaning sheet 17 shown in FIGS. 3( a)and 3(b), a semiconductor chip 24 is set in the cavity 6 of the mold 28,followed by supplying a molding resin in the cavity 6 in the same manneras in the above-stated molding method to resin mold this semiconductorchip 24.

When using the mold cleaning sheet of Embodiment 1 and the method ofproducing a semiconductor device by use of the sheet, the followingfeatures and effects are obtained.

More particularly, since the through-hole 17 a corresponding to thecavity 6 is formed in the cleaning sheet 17, the cleaning resin 25 canpass through the through-hole 17 a of the cleaning sheet 17 upon supplyand charge of the cleaning resin 25 to the cavity 6. In this condition,the flow of the cleaning resin 25 within the cavity is not impededirrespective of the existence of a filler contained in the cleaningresin 25 and the resin charging pressure, thereby permitting thecleaning resin 25 to be distributed to all corners.

As a result, the cleaning resin 25 distributed to all corners of thecavity 6 can remove the dirt in the corner of the cavity 6.

In this way, the cavity 6 of the mold 28 can be satisfactorily cleaned,thereby improving the cleaning effect.

Because the cleaning sheet 17 entirely covers the faces 26 of the mold28 upon cleaning, the cleaning resins 25 in the cavity 6, the faces 26(parting faces), the cull 7 and the gate 13 are combined togetherthrough the cleaning sheet 17, so that when the cleaning sheet 17 isremoved after curing of the cleaning resin 25, the resin can bewithdrawn integrally without separation into pieces on the cleaningsheet 17.

Accordingly, the cleaning sheet 17 can be readily attached to ordetached from the mold 28. This allows the cleaning sheet 17 aftercleaning to be handled simply.

Eventually, the time of the cleaning work using the cleaning sheet 17can be shortened.

Because the cleaning sheet 17 entirely covers the faces 26 of the mold28, the dirt at the inlet of the pot 9 of the mold 28, the area aroundthe cull 7, air vent 14 and the like can be removed with the cleaningresin 25 sticking to the cleaning sheet 17. In addition, resin burrs canalso be removed, thereby reducing the working time appreciably.

Further, because the cleaning sheet 17 entirely covers the faces 26 ofthe mold 28, it is possible to clean portions which are not in contactwith the cleaning resin 25 in the mold 28.

Irrespective of the number of the lead frames set in the mold 28, thefaces 26 of the mold 28 can be entirely covered with one cleaning sheet,highly precise positioning of the cleaning sheet 17 relative to the mold28 is not necessary.

In this connection, when a cleaning sheet 17 made of a nonwoven fabricis used in Embodiment 1, it is not necessary to machine the mold 28 tomake positioning pins and positioning pin holes as conventionallyrequired in the case using a dummy lead frame.

This leads to the reduction in cost of the mold 28.

Since any dummy lead frame is not used, the mismatch ascribed to theshift of the dummy lead frame de not occur.

Since the faces 26 of the mold 28 are entirely covered with one cleaningsheet 1, only one cleaning sheet 17 is set in position irrespective ofthe number of lead frames set within the mold upon molding. Thus, thecleaning work is performed at low costs.

By using the cleaning sheet 17 of Embodiment 1, since the expensivedummy lead frame is not used, the cleaning work in the mold 28 isperformed at low cost.

Because the cleaning sheet 17 has the through-hole 17 a corresponding tothe opening 6 a of the cavity 6 and entirely covers the faces 26 of themold 28 upon cleaning, the cleaning effect can be improved withoutlowering the workability of cleaning.

It will be noted that in the procedure of producing a semiconductordevice such as QFP 19 of Embodiment 1, the cleaning work of the mold 28can be reduced appreciably, thereby improving the cleaning effect of themold 28 and the productivity of the semiconductor device.

Next, Embodiment 2 of the invention is described.

In Embodiment 2, a variation of the mold cleaning sheet used in thecleaning step of the mold shown in FIG. 2 is described.

A cleaning sheet (mold cleaning sheet) 29 shown in FIG. 7 is formed withthrough-holes 29 a corresponding to the cavities 6 of the mold 28 andalso with a slit 29 b at the corners of a periphery of each through-hole29 a and a cut such as a flow cavity cut 29 c.

The through-hole 29 a has a size substantially equal to or slightlysmaller than the cavity 6 of the mold 28.

The slits 29 b and the flow cavity cut 29 c are, respectively, formed atportions corresponding to the flow cavities (recesses) communicatingwith the cavities 6 of the second mold half 4, of which the flow cavitycuts 29 c are ones formed substantially in the same shape as the flowcavity 27.

The flow cavity 27 permits air or the molding resin within the cavity 6to be escaped, so that air entrainment from the gate 13 is prevented andthe molding resin in the cavity is filled in a well-balanced condition.

Accordingly, when the mold 28 is cleaned, the slits 29 b and the flowcavity cut 29 c are provided for ensuring satisfactory filling of thecleaning resin 25, shown in FIG. 5, relative to the flow cavities 27 andthe air vents 14 which are recessed portions communicating to thecavities 6.

More particularly, when the cleaning resin 25 is poured into the cavity6, the cleaning resin 25 is filled in the cavity 6 through thethrough-hole 29 a of the cleaning sheet 29. At the corners of the cavity6, the cleaning resin 25 flows into the flow cavities 27 and the airvents 14 through the flow cavity cut 29 c and the slits 29 b.

In this way, the cleaning resin 25 can cling to the cleaning sheet 29via the flow cavity cut 29 c and the slits 29 b, and thus cleaning resin25 can be filled in the flow cavities 27 and the air vents 14.

As a consequence, the cleaning resin 25 after hardening thereof can beremoved from the second mold half 4 while removing the cleaning sheet 29from the mold 28.

It will be noted that as to whichever the slit 29 b is formed as a cutor the flow cavity cut 29 c is formed, the cleaning resin 25 isrelatively unlikely to flow into the flow cavity 27 that is located at aposition distant from the gate 13 of the second mold half 4, and thusthe flow cavity cut 29 c, not the slit 29 b, should be favorably formed.

Since the cleaning resin 25 is relatively likely to flow into the flowcavity 27 at the side of the gate 13, the slit 29 b is formed in thiscase.

Thus, with the variation shown in FIGS. 7 and 8 (i.e. the cleaning sheet29 for QFP 19 shown in FIG. 6), only the flow cavity 27 located mostremotely from the gate 13 is constituted as the flow cavity cut 29 c,and the slit 29 b is formed at the other three corners.

In contrast thereto, another variation shown in FIG. 9 (i.e. a cleaningsheet 29 for QFP 19 shown in FIG. 6) shows the case where the slit 29 bis formed at four corners. As will be apparent from this, it is notcritical to form the flow cavity cut 29 c (see FIG. 7) and the slits 29b at whichever corners. Likewise, the width and length of the slit 29 cor the shape of the flow cavity cut 29 b is not critical.

It will be noted that the type of material for and the thickness of thecleaning sheet 29 of Embodiment 2 are similar to the cleaning sheet 17of the foregoing Embodiment 1.

Other structures of the cleaning sheet 29 of Embodiment 2 and the methodof producing a semiconductor device using the cleaning sheet 29 are,respectively, similar to those of Embodiment 1 including the method ofproducing a semiconductor device using the cleaning sheet 17 illustratedin Embodiment 1, and are not repeatedly set forth herein.

According to the cleaning sheet 29 of Embodiment 2 and the method ofproducing a semiconductor device using the same, when the cleaning resin25 is charged into the cavity 6 when cleaning the mold 28 shown in FIG.2, the cleaning resin 25 can be made to pass to the slits 29 b and theflow cavity cut 29 c of the cleaning sheet 29.

This permits the cleaning resin 25 to be filled in the recesses such asthe flow cavities 27 and the air vents 14 upon cleaning, and thecleaning resin 25 can be stuck and attached to the cleaning sheet 29through the cuts.

Accordingly, after hardening of the cleaning resin 25, the release ofthe cleaning sheet 29 from the second mold half 4 causes the cleaningresin 25 being filled in the recesses (the flow cavities 27 and the airvents 14) at the face of the second mold half to be removed. Thus, thecleaning effect of the recesses can be improved and the cleaning resin25 ca be reliably removed along with the cleaning sheet 29, resulting inthe easy removal of the cleaning resin 25 from the recesses.

This entails the reduction in cleaning time of the mold using thecleaning sheet 29.

It is to be noted that when the cuts such as the flow cavity cut 29 cand the slid 29 b, which correspond to the recesses at portions(portions relatively remove from the gate 13) opposite to the gates 13of the second mold half 4, are shaped in conformity with the recesses,the cleaning effect of the recesses can be further improved.

Next, Embodiment 3 of the invention is now described.

In Embodiment 3, a variation of a mold cleaning sheet used in thecleaning step of the mold 28, shown in FIG. 2, in the production of thesemiconductor device illustrated in Embodiment 1 is described, likeEmbodiment 2.

More particularly, a framed cleaning sheet (molding cleaning sheet) 30shown in FIGS. 10( a) and 10(b) includes, like the cleaning sheet 17illustrated in the foregoing Embodiment 1, a cleaning sheet 30 a whichentirely covers the face 26 of the mold 28 and has through-holes 30 b atportions corresponding to the cavities 6, and a framed reinforcing sheet30 c which is positioned along a marginal portion 26 a of the face 26 atthe outside of a plurality of cavities 6 in the face 26 of the mold.

It will be noted that the through-holes 30 b formed in the cleaningsheet 30 a have a size substantially equal to or slightly larger thanthat of the cavity 6 of the mold 28.

When the cleaning resin 25 (see FIG. 5) is charged upon cleaning of themold 28 as shown in FIG. 12, the framed cleaning sheet 30 of Embodiment3 increases a clamping force at the outside of the cavities 6 uponclamping of the mold 28 of the second mold half serving as a low moldhalf and the first mold half serving as a top mold half so that thecleaning resin 25 is prevented from leakage from the faces 26 of themold 28.

More particularly, as shown in FIGS. 10( a) and 10(b), the framedcleaning sheet 30 includes a cleaning sheet 30 a having through-holes 30b corresponding to the cavities 6 shown in FIG. 11 formed therein, and aframed reinforcing sheet 30 c which can be arranged along the marginalportion 26 a of the face 26 at the outside of each of a plurality ofcavities 6 in the face 26 of the second mold half 4, both sheets beingbonded together.

When the mold 28 is cleaned, the cleaning sheet 30 a is so arrangedentirely over the face 26 that the through-holes 30 b of the cleaningsheet 30 a are set in conformity with the cavities 6, and the framedreinforcing sheet 30 c is arranged on the face 26 along the marginalportion 26 a of the face 26 at the outside of the plural cavities 6 ofthe framed reinforcing sheet 30 c.

It will be noted that the framed cleaning sheet 30 of Embodiment 3 isone wherein the cleaning sheet 30 a and the reinforcing sheet 30 c havebeen preliminarily bonded together as shown in FIGS. 10( a) and 10(b),so that when used for cleaning, the framed cleaning sheet 30 is placedon the face 26 of the second mold half 4.

Thereafter, as shown in FIG. 12, the cleaning sheet 30 a and thereinforcing sheet 30 c are clamped between the first mold half 3 and thesecond mold half 4, after which the cleaning resin 25 is poured into thecavities 6 under clamped conditions to fill the cleaning resin 25 in thecavities. After hardening of the cleaning resin 25, the cleaning resin25 is removed from the faces 26 of the mold 28 along with the cleaningsheet 30 a to clean the mold 28.

It will be noted that upon molding of a semiconductor device, such asSOP having a relatively elongated, molded portion 22 (see FIG. 6although the QFP 19 shown in FIG. 6 has the molded portion 22 that issubstantially square) or QFN having a matrix frame, if the faces 26 ofthe mold 28 are so arranged that the distance (L in FIGS. 11 and 12)between the outer edge of the cavity 6 and the marginal portion 26 a ofthe face 26 is relatively smaller (e.g. if L is 10 mm or below), thecleaning resin leaked from the cavity 6 upon cleaning of the mold 28runs out of the mold cleaning sheet and may attach to over side surfacescontiguous to the faces 26 of the mold 28. In this sense, the framedcleaning sheet 30 shown in FIGS. 10( a) and 10(b) is more effective whenused for cleaning the mold 28 for SOP or QFN wherein the above-indicatedL is 10 mm or below.

The framed reinforcing sheet 30 c has, for example a thickness of about0.1 to 0.2 mm and should be preferably formed of a nonwoven fabric,paper, copper or a fluorine resin.

Moreover, like the framed cleaning sheet 30 of Embodiment 3, thecleaning sheet 30 a and the reinforcing sheet 30 c may be preliminarilybonded together. Alternatively, both may not be bonded together and maybe separately provided, after which upon cleaning, the sheets aresuccessively placed on the face 26 of the mold 28, followed by moldingfor cleaning.

The framed cleaning sheet 30 of Embodiment 3 is effective forapplication to a semiconductor device other than SOP or QFN but using amatrix frame or also to BGA using a tape substrate.

It is to be noted that the type of material and thickness of thecleaning sheet 30 a of the framed cleaning sheet 30 of Embodiment 3 aresame as those of the cleaning sheet 17 of Embodiment 1.

Further, the method of producing a semiconductor device using the framedcleaning sheet of Embodiment 3 is not repeatedly described hereinbecause the method is substantially same as the method of producing asemiconductor device using the cleaning sheet 17 illustrated inEmbodiment 1.

According to the framed cleaning sheet 30 of Embodiment 3 and the methodof producing a semiconductor device using the same, when the mold 28 iscleaned, each through-hole 30 b of the cleaning sheet 30 a of thecleaning sheet 30 is arranged over the face 26 correspondingly to eachcavity 6 and the reinforcing sheet 30 c is disposed at the face 26 alongthe marginal portion 26 a of the face 26 at the outside of pluralcavities 6. In this condition, the framed cleaning sheet 30 is clampedbetween the first mold half 3 and the second mold half 4 of the mold 28for cleaning, and thus the clamping force of the mold 28 can beincreased. As a result, the leakage of the cleaning resin 25 from thefaces 26 of the mold 28 can be prevented upon cleaning.

Accordingly, the cleaning resin 25 is prevented from attaching to thesides of the mold 28, thus saving the trouble of removing the resin. Asa result, the cleaning work efficiency of the mold 28 ca be improved.

The use of the framed cleaning sheet 30 attached with the reinforcingsheet 30 c prevents the cleaning resin 25 from leaking from the faces 26of the mold 28 upon cleaning. Accordingly, the cleaning resin 25 can bewell filled in the recesses such as the cavity 6 and the flow cavitycuts 29 c (see FIG. 8). This leads to an improved cleaning effect of therecesses such as the cavity 6, the flow cavity cuts 29 c and the like.

Especially, when the distance between the outer edge of the cavity inthe mold 28 and the marginal portion 26 a of the face 26 is relativelysmall (e.g. where the distance L shown in FIG. 11 is 10 mm or below),the framed cleaning sheet 30 having the reinforcing sheet 30 c is mosteffective.

The use of the framed cleaning sheet 30 having the reinforcing sheet 30c can appropriately prevent leakage of the cleaning resin 25 from thefaces 26 of the mold 28 upon cleaning and thus ensures attachment anddetachment of the framed cleaning sheet 30 relative to the faces 26 ofthe mold 28.

Further, where the cleaning sheet 30 a is made of a nonwoven fabric, theexpansion and contraction of the cleaning sheet 30 a can be preventeddue to the use of reinforcing sheet 30 c. This eventually leads to afurther improvement in the cleaning work efficiency of the mold 28.

The invention made by the present inventors has been particularlydescribed based on the embodiments of the invention, which should not beconstrued as limiting the invention thereto, and many modifications maybe possible without departing from the spirit of the invention.

For instance, in the foregoing Embodiments 1, 2, 3, the case where thecleaning sheets 17, 29, 30 a are, respectively, formed of a nonwovenfabric, the material for the cleaning sheets 17, 29, 30 a is not limitedto a nonwoven fabric and may include paper, other type of cloth and thelike.

The thickness of the cleaning sheets 17, 29, 30 a is not limited to thatillustrated in the foregoing Embodiments 1, 2, 3 and those sheets havingdifferent thicknesses may also be used.

Moreover, with respect to the size of the cleaning sheets 17, 29, 30 a,the sheets may be slightly smaller than the face 26 provided that thesize is sufficient to cover substantially all of the face 26 of the mold28.

As for the through-holes 17 a, 29 a, 30 b formed in the cleaning sheets17, 29, 30 a, respectively, the shape and the number of the holes arenot limited to those of the foregoing Embodiments 1, 2, 3, and variousforms and different numbers of though-holes may be used. Thethrough-hole may be substantially equal in size to the opening 6 a ofthe cavity 6 or may be larger or smaller than the opening 6 a of thecavity 6 provided that the cleaning resin 25 is able to passtherethrough.

It will be noted that the mold 28 of the foregoing Embodiments 1, 2, 3may have multiple lead frames arranged in line or may have a matrixframe. In either case, the cleaning work can be performed at low costs.

In the foregoing Embodiments 1, 2, the case where the semiconductordevice molded by means of the transfer molding apparatus shown in FIG. 1is QFP 19 shown in FIG. 6 has been set forth, and the semiconductordevice is not limited to the QFP 19. For instance, other types ofsemiconductor devices such as SPO may be used so far as they are moldedwith the transfer molding apparatus.

Further, although the mold 28 of the foregoing Embodiments 1, 2, 3 hasbeen illustrated such that the first mold half 3 is a top mold half andthe second mold half 4 is a bottom mold half, the first mold half 3 maybe provided as a bottom mold half and the second mold half 4 provided asa top mold half.

INDUSTRIAL UTILITY

As stated hereinabove, the mold cleaning sheet of the invention and themethod of producing a semiconductor device using the sheet can improvethe cleaning effect of a mold and are suited for improving theproductivity of a semiconductor device.

1. A method of manufacturing a semiconductor device comprising the stepsof: (a) providing a mold having a first mold, a first cavity formed onthe first mold, a gate connected to the first cavity, a flow cavityconnected to the first cavity, and a second mold opposed to the firstmold; (b) disposing a lead frame with a semiconductor chip between thefirst and second molds such that the semiconductor chip is arrangedinside of the first cavity, supplying an encapsulating resin into thefirst cavity through the gate, and sealing the semiconductor chip withthe encapsulating resin; and (c) disposing a cleaning sheet between thefirst and second molds, supplying a cleaning resin into the first cavitythrough the gate, and cleaning the mold, wherein the first cavity in aplan view is a quadrangle, wherein the gate is connected to a firstcorner portion, wherein the flow cavity is connected to a second cornerportion opposing to the first corner portion via a central portion ofthe first cavity in the plan view, wherein the cleaning resin has afiller, wherein in the step (b), the encapsulating resin is suppliedinto the flow cavity through the first cavity, wherein in the step (c),the cleaning sheet is disposed between the first and second molds suchthat the cut portion is overlapped with the flow cavity in the planview, and wherein in the step (c), the cleaning resin is supplied intothe flow cavity through the first cavity and the cut portion.
 2. Amethod of manufacturing a semiconductor device according to claim 1,wherein the first mold has an air vent formed at a third corner portionof the first cavity and connected to the first cavity, and wherein inthe step (b), air remaining in the first cavity is pushed out throughthe air vent.
 3. A method of manufacturing a semiconductor deviceaccording to claim 2, wherein the cleaning sheet has a slit, wherein inthe step (c), the cleaning sheet is disposed between the first andsecond molds such that the slit is overlapped with the air vent in aplan view, and wherein in the step (c), the cleaning resin is suppliedinto the air vent through the first cavity and the slit.
 4. A method ofmanufacturing a semiconductor device according to claim 2, wherein thesecond mold has a second cavity opposing to the first cavity.